1. Technical Field of the Invention
The present invention relates to a tire having a radial carcass reinforcement, and more particularly to the structure of the beads of the tire. Still more particularly, the invention relates to a tire in which at least one of the beads has a structure which permits modification of the clamping of the bead on its rim according to the tension of the carcass reinforcement, and in particular an increase thereof when the inflation pressure increases up to its rated value.
2. The Related Art
A tire of the aforementioned type, which has the special feature of overcoming the problems of rotation on the rim while remaining easy to mount and dismount, is described in U.S. Pat. No. 5,971,047. Such tire, which is mounted on its rim and inflated to its operating pressure, comprises a radial carcass reinforcement, viewed in meridian section, which is wound in at least one bead around at least one bead wire coated with rubber mix, from the heel to the toe of the bead, to form an upturn extending in a profiled element of rubber mix in the form of a wedge defined by two sides coming from an apex located beneath the section of the coated bead wire. The radially outer side forms, with a line parallel to the axis of rotation passing through the apex, an acute angle xc3x81, open radially towards the outside, and the radially inner side forms with the parallel line an acute angle xc3x82, open radially towards the inside. The rubber mix forming the profiled element, axially adjacent to the bead wire, has a Shore A hardness greater than the Shore A hardnesses of the rubber mixes located axially and radially above the bead wire and the profiled element.
Although the invention described and claimed in the ""047 patent referred to above applies whatever the inclination of the bead seat, it is particularly beneficial in the case of seats inclined towards the outside of the tire, the toes of the beads then being to the outside.
Likewise, the carcass reinforcement upturn preferably has a length such that it is in contact with the total perimeter of the profiled element or wedge. It thus forms the two, radially outer and inner, edges of the rubber profiled element and the side opposite the apex or center of the profiled element. The end thereof is located axially beyond the point of intersection of the two, outer and inner, sides. The part of the upturn immediately adjacent to the part of the upturn which is wound about the bead wire can form, firstly, the radially outer side of the profiled element or wedge, then the side opposite the apex of the profiled element, and then finally the radially inner side of the profiled element, ending beyond the junction point of the two, outer and inner, sides. It may also first form the radially inner side of the profiled element or wedge, then the side opposite the apex of the profiled element, and then finally the radially outer side of the profiled element, ending in the same manner as previously described.
The operations of mounting and dismounting such tires having bead seats inclined towards the outside require the use of mounting and/or dismounting levers. Such a use involves cutting the protective rubber mix of the beads, more particularly in the zone of the bead seats. The cuts are propagated during travel towards the reinforcement elements of the carcass reinforcement and cause such elements to be bared, with breaking the elements. The cuts furthermore reach the reinforcement elements themselves in many cases. In any case, the degradation of the reinforcement elements following such cuts allows the inflation gas, air and humidity to infiltrate into the elements, resulting in separation between reinforcement elements and the rubber calendering layer covering them. The separations are revealed by the presence of pockets of varying sizes on the sidewalls of the tire.
The object of the invention is a solution for overcoming the above drawbacks.
In accordance with the invention, a tire is provided having at least one bead seat inclined towards the outside and a radial carcass reinforcement wound within said bead around a bead wire from the heel to the toe of the bead to form an upturn, the edge of which, viewed in meridian section, is located on the radially outer face of a profiled element of rubber mix, axially and externally adjacent to the bead wire. The profiled element, viewed in meridian section, has the shape of a drop of water with an apex located beneath the section of the bead wire, and a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes located axially and radially above the bead wire/profiled element assembly. The carcass reinforcement upturn is extended by a reinforcement armature which surrounds the profiled element and which is turned up about the bead wire, the upturn of the carcass reinforcement and the reinforcement armature overlapping over an axial distance at least equal to half the axial width of the bead seat, and the radial distance between respective reinforcement elements of the two reinforcements being at least equal to 0.6 mm.
As used herein, the term xe2x80x9cshape of a drop of waterxe2x80x9d is to be understood to mean a geometric shape approaching the shape of a circular sector, that is to say, a sector defined by two sides or radii departing from an apex or center of the sector, the two ends of the two sides defining a third circular side opposite the apex. The shape of a drop of water differs from the theoretical shape of such a sector by the fact that the two sides coming from the apex may be curved, and that the circular side opposite the apex is either at a tangent to the other two sides, or joined to the other two sides by arcs of a circle which are tangent. The profiled element in the shape of a drop of water is located between two straight half-lines which are tangent to the anchoring bead wire coated with rubber mix and to the carcass reinforcement: the first half-line forms with a line parallel to the axis of rotation an angle which is open radially towards the outside and which may be between 40xc2x0 and 80xc2x0, the second half-line forms with a line parallel to the axis of rotation an angle which is open towards the inside and which may be between 0xc2x0 and 30xc2x0, and the two half-lines are secant at a point which is the apex of the drop-of-water shape.
The constitution of the reinforcement armature of the profiled element may be different from the constitution of the carcass reinforcement, and may be obtained in various way. The difference may advantageously lie, for example,
in the number of plies respectively forming the two reinforcements: the number of plies being greater in the reinforcement armature of the profiled element;
in the use in the reinforcement plies of the profiled element of reinforcement elements which differ in their modulus and/or in their nature: use of textile elements in the carcass reinforcement and of elastic metal elements in the bead reinforcement armature;
in the use of spacing between adjacent reinforcement elements which are different for the two reinforcements: the reinforcement elements of the reinforcement ply of the profiled element are closer to each other than are the elements of the carcass reinforcement;
in the use for calendering of the respective reinforcement elements of the two reinforcements of rubber mixes which differ in their composition and/or elasticity modulus, for example, shearing modulus; and
in the orientation, relative to the circumferential direction, of the reinforcement elements of the two reinforcements.
Advantageously, the rubber mix forming the drop-of-water-shaped profiled element, axially adjacent to the bead wire, will have a Shore A hardness at least equal to 65 (measured in accordance with ASTM Standard D.67549T).
Preferably, the bead wire is of the braided type, that is to say, a bead wire formed of a core around which are wound (a) cord(s) or cable(s) in one or more layers. As is known per se, the layer(s) of cord(s) or cable(s) are able to turn about the core.
The bead wire reinforcing the bead is surmounted radially to the outside by a substantially triangular profiled element of rubber mix preferably having a Shore A hardness of less than 50. The space located, on the one hand, axially adjacent to the profiled element radially surmounting the bead wire and, on the other hand, radially adjacent to the profiled element or wedge axially next to the bead wire is filled with a third profiled element of rubber mix of substantially triangular shape, such mix also having a Shore hardness of less than 50.
The reinforcement armature of the profiled element surrounds the profiled element and is turned up about the bead wire, the latter already being covered by the carcass reinforcement. It is advantageous for the radial distance between the respective reinforcement elements of two adjacent plies of the two reinforcements to be at least equal to 0.9 mm beneath the bead wire. This excess thickness permits additional protection of the carcass reinforcement.